BLVII-46 Created ARRoiStatsPairFactory and modified ROI Provider behaviour.

There was a design flaw in that the Stats plugin needed to know if the roi plugin was enabled and if so its name to prepend to its data.

A few tests need fixing. [Committed during beamline commisioning!]
EPICS: To remove the wrong 'InputNames' from EpicsQuadraCurrentAmplifier.
EPICS: To use the caput callback when change the EpicsQuadraCurrentAmplifier gain.